The present invention relates to the technical field of building of habitations and/or factories, as well as of more complex building works such as building of tunnels, submarine structures and the like.
More particularly, the present invention aims to provide for a leakproofing article to be used in the building of habitation and or factory structure foundation, or for building of underground structures and/or tunnels, as well as in the more difficult technical field of submarine works.
The present invention may be mainly applied in the general technical field of building.
The use of bentonite as leakproofing material in the field of building is well known in the art.
For instance, it is used in the building of foundation and/or in any other type of application in which a suitable degree of imperviousness to water has to be assured.
It is also known that sodium natural bentonite is a clay which undergoes a substantial hydration when it comes into contact with water, said hydration increasing the bentonite volume up to thirty times its dry volume.
As a consequence of the hydration process, it is known that the bentonite produces both a gel phase of the colloidal type, which causes an increase of the bentonite volume of about 10-15 times with respect to its dry volume, and a solute phase, which causes an even greater increase of the bentonite volume.
Bentonite is used in the form of particles, generally placed inside of one or more layers of corrugated card-board sheets or of needled non-woven fabrics, obtaining a structure similar to a panel and/or a small mattress which is set at the extrados of underground structures foundation and/or at any other location where a leakproofing barrier is needed.
A further solution known the art provides for the use of bentonite coupled with a suitable binder, e.g. butylic rubbers and/or water-soluble glues.
In this case, the system binder/bentonite is given a rolled shape or a panel type shape to so that it can be sufficiently handy and easy to be laid.
For instance, U.S. Pat. No 4,048,373 discloses a solution of the type cited above according to which a leakproofing panel is produced, said panel being formed by two sheets, advantageously card-board sheets, suitably spaced in order to contain bentonite together with a suitable additive.
In general, said additive is constituted by a water-soluble dispersant, e.g. a water-soluble salt of acetic or phosphoric or boric acid, combined with a water-soluble polymer, for instance polyacrylic acid, water-soluble salts of polyacrylic acid, polyacrylnitril, polyvinylacetate, polyvinylalcohol or copolymer thereof, according to defined percentages of the components of the bentonitic composition.
According to a preferred form of embodiment disclosed in U.S. Pat. No. 4,048,373, the leakproofing panel is constituted by two corrugated card-board sheets and by a corrugated paper band which is placed between them.
Said paper band comes into contact with the two sheets forming a plurality of voids which are filled with the bentonitic composition mentioned above.
U.S. pat. No. 4,048,373 discloses a water impervious panel comprising one upper and one lower sheets, said sheets being made of one of one of a range of polymers. A shortcoming of the above document is that the dissolution rate is not predetermined and controlled, theref ore there may be found to occur the expansion of the bentonite pack at undesired times, and the only thing that can be relied upon in that respect is carrying out the operations in an extremely expedite way, which is not always possible whereas it is always to the detriment of accuracy and safety, and does not rule out t he risk that the expansion takes place when the panels are still being worked upon.
Moreover, the panel disclosed in the above document is not structurally feasible, as the water swellable material is simply laid upon its solid support, therefore it is prone to structural failure.
In the present application the bulk impermeable material is found to be spread over an inner layer made of biodegradable kraft paper that has characteristically such a shape that it confers the device an overall inherent resilience and resistance, therefore a particular suitability for use in the building industry as there are no risks for it to suffer from structural failures even when the water swellable material has not set.
Furthermore, the dissolution rate of the coating can be controlled with extreme precision.
EP-A-567,692 discloses a clay-based impermeable material to be used in the building industry, made of sodium or calcium bentonite, and applied to a support, said material fulfilling its function on account of the fact that the sodium or calcium bentonite is coated with a degradable and temporarily water resistant coating, made of cellulose. The durability of the coating disclosed in the above document depends on its thickness, as after contact with water, it breaks down at a constant rate. Therefore if a material with a relatively long temporary surface impermeability is desired, then encumbering volumes of the surface coating must be used, thing which in certain cases may turn out to be detrimental for the stability of the whole building, as, after dissolution, free voids are left to bear considerable weights. Another shortcoming of the disclosure of the above document is that because the bentonite is simply laid upon its support, it is inherently of limited resilience and resistance.
In other words, this document does not disclose any means for keeping under control the water-solubility of the material constituting the coating layer of the leakproofing article.
U.S. Pat. No. 4,565,468 discloses a device for providing a moisture impervient barrier comprising a base sheet member with a bentonite layer on its upper surface, and a top sheet member positioned over the bentonite.
The top sheet member is constituted of a material pervious to water so as to permit hydration of the bentonite.
The present invention aims to solve the problem constituted by a quick, premature and uncontrollable hydration undergone by granular sodium bentonite when it contacts water, which can be rain water and/or water coming from a water-bearing stratum or from concrete, during particular structure building steps.
Said casual and premature bentonite hydration is often extremely negative as regards to the final result of the structure which has to be built and to the realization of an effective leakproofing barrier.
In fact, if the bentonite hydration process occurs before the concrete structure is laid, and the obtained structure can result as being defective; the consequent effects deriving therefrom can be deleterious for the building.
On the other hand, if the bentonite hydration occurs when the concrete has just been cast, the increase in the bentonite volume can exert a harmful pressure on the concrete which does not have a sufficiently high mechanical resistence yet, thereby causing permanent damages to the building structure.
Furthermore, it may happen that the hydrate bentonite, i.e. the expanded bentonite, soils and muddies the concrete reinforcements causing adhesion problems which determine the iron being uncoupled from the concrete, which phenomenon is known under the name of reduction or zero setting of the iron/concrete matrix.
Thus, said drawbacks produce remarkable and often irreversible damages both to the leakproofing system and to the structure which has to be built.
This means that works must be stopped and a new leakproofing barrier made of bentonite is needed to be laid, thereby causing a loss of time and an increase of the costs.
The realization of water-soluble plastic and completely biodegradable films, e.g. films based on polyvinylic alcohol (PVOH), to be used in very different applications, is also known in the art.
For instance, said articles can be advantageously used as protective colloids of numerous chemical components, particularly in paper and textile fields; as light polarizing filters; as temporary sizes in textile yarns production; as main components in the production of the envelopes of medicinal capsules; as supports for photosensitive elements of television screens.
The present invention aims to set aside the disadvantages and drawbacks which are typical of the background art and to provide for a suitable leakproofing article to be used both in the building of the foundation of habitation and/or factory structures, and in the realization of complex works, such as tunnels, submarine structures and the like.
This is obtained by means of a leakproofing article having the features disclosed in claim 1.
The dependent claims describe particularly advantageous forms of embodiment of the leakproofing article according to the present invention.
The present invention allows to produce a leakproofing article of any suitable shape and dimensions according to any specific need, the leakproofing function being carried out, for instance, by means of granular sodium bentonite acting as active leakproofing element.
According to the present invention, the granular sodium bentonite is introduced into a specific envelope constituted by a film made of water-soluble material, said film being able to delay the start of the bentonite hydration process for a suitably long time which is previously fixed on the base of particular building requirements.
The leakproofing effect described above is advantageously achieved by using bentonite and/or bentonitic compositions, but any other leakproofing material can be used to carry out the present invention.
According to a further form of embodiment, ion exchange resins and/or colloid modifiers, e.g. carboxymethylcellulose, can advantageously be mixed to said leakproofing article.
According to the present invention, the bentonite or the bentonitic composition, used to obtain a leakproofing barrier, becomes insensitive to rain water and/or water-bearing stratum permeations and/or to the water coming from the concrete for the period of time which is needed for laying the leakproofing barrier and for carrying out the subsequent concrete casting operation, thereby avoiding the drawbacks cited above.
Said temporary imperviousness to water is obtained by coating the bentonite with a film made of water-soluble material, said film being able to shield the bentonite from water for a predetermined period of time (for instance from 1 up to 30 days after the occured contact with water).
In such a way the bentonite hydration process, and the consequent activation of the leakproofing effect, can occur in the most suitable instant of time, thereby avoiding damages to the building structure so that the effectiveness of the leakproofing barrier is not compromised.
According to the present invention a water-soluble film advantageously usable to achieve the above-cited object of the invention is constituted by an article known under the trademark HYDROLENEO LTF, produced by IDROPLAST S.p.A., Italy.
HYDROLENE(copyright) LTF is a water-soluble and biodegradable film with a thermoplastic composition consisting of about 75% of polyvinylalcohol at high molecular weight and average hydrolysis degree (86-88%), while the remaining 25% consists of polyoilic plasticizers and process additives, notably of organic nature.
Generally, said plasticizers are aliphatic high-boiling polyoils selected from the group comprising natural or synthetic alcohols and/or alcohol-ethers containing at least three carbon atoms per molecule and at least two primary or secondary alcoholic functional groups.
HYDROLENE(copyright) LTF water-solubility is controlled by acting on a plurality of parameters.
First of all, it is necessary to remark that the HYDROLENE(copyright) LTF water-solubility rate strongly depends on the temperature of the water contacting it.
For instance, FIG. 4 shows the flow of the water-solubility rate with respect to the temperature in the case of a type of HYDROLENE(copyright) LTF.
This curve points out a particular temperature value, called WST temperature (Water Solubility Temperature), which divides the graph into two distinct zones (zone A and zone B), said value representing the temperature at which HYDROLENE(copyright) LTF completely solubilizes in water.
As it is shown in FIG. 4, the HYDROLENE(copyright) LTF water-solubility rate increases very slowly with the temperature in zone A; on the contrary, when the WST value is reached, the curve passes from zone A to zone B where the HYDROLENE(copyright) LTF water-solubility rate quickly increases with temperature.
A curve similar to that of FIG. 4 can be obtained taking into consideration the HYDROLENE(copyright) LTF water-solubility rate compared to time.
Thus, when both the water temperature and the period of time after which the hydration have to occur are fixed, to keep working inside of zone A it is necessary to modify the chemical formulation of HYDROLENE(copyright) LTF by using plasticizers and/or shield agents, even combined together.
In fact, said components retain the oxydrilic groups of the polyvinylalcohol allowing the starting time of the polymeric chains breaking reaction to be controlled, while the temperature controls the reaction kinetics.
In order to keep working in zone A, a suitable plasticizer in a given quantity (e.g., on the base of its viscosity and its binding properties), as well as a suitable shielding agent have to be selected.
Furthermore, having defined with (1)
xe2x80x94(CH2-CHOH)nxe2x80x94(CH2-CHOCOCH3)mxe2x80x94xe2x80x83xe2x80x83(1)
a generic formulation of a polyvinylalcohol obtained by a controlled hydrolysis of the polyvinylacetate, in which formulation n indicates the alcoholic groups and m indicates the acethylic groups, it is possible to control the water-solubility of said polyvinylalcohol, remarkably lowering it, by using alcohols having n/m rate values higher than 95/5.
Other water-soluble articles based on polyethylene, polycaprolactone, maize amid and other articles similar to HYDROLENE(copyright) LTF, i.e. having a polyvinylalcoholic base, can be used as envelopes for the leakproofing material.
As said before, the leakproofing article according to the present invention can be obtained in different dimensions, thicknesses and shapes in order to be suitable for any building type and requirement.
According to a first form of embodiment, said leakproofing article has a panel-like shape having standard dimensions in accordance with the specific use it is addressed to.
Said panel it is constituted by an inner layer, advantageously made of biodegradable kraft paper having a honey-comb shape in order to contain the bentonite and/or the bentonitic composition and to maintain it uniformly distributed on the whole panel surface.
This uniformity is very important since the granular sodium bentonite is characterized by a very variable granulometry which requires a given weight for square meter dosage of the bentonite (e.g. Kg/m2) in order to obtain a gel omogeneously distributed on the whole surface to be made impervious to water when the hydration process has occured.
Said gel should advantageously be distributed on the surface to be made impervious as uniformly as possible; actually, thanks to a complete and immediate adhesion to the concrete, it determines the formation of a gel/concrete matrix which prevents a migration of water to the concrete/leakproofing interface.
Moreover, if a mistake occurs during the laying operation of the barrier, or in the case where fissures are formed in the concrete, the gel adhesion to the concrete allows the point where the loss has occured to be exactly singled out, and in this way it is possible to quickly and efficiently operate in a simple and safe way on the damaged area.
The weight dosage of the bentonite allows granular sodium bentonite to be used, having any granulometric distribution.
Thus, in a simple and precise way it is possible to obtain leakproofing articles having a different total permeability rate (K) since, using a bentonite of the same quality, said rate is proportional to the bentonite weight for each square meter of surface to be made impervious to water.
Besides, it is also possible to obtain articles having a different thickness on the base of the bentonite quantity which is used, thereby realizing articles having a suitable permeability relative to the specific hydraulic gradient.
Furthermore, the inner layer honey-comb structure of this panel-shaped form of embodiment allows the bentonite to be kept uniformly distributed when the panel is vertically placed or during its transport and/or when assemblying the leakproofing barrier.
Moreover, the honey-comb structure gives the panel the necessary mechanical strength for being used.
Furthermore, said inner layer is wrapped on both sides by means of a water-soluble plastic film which is suitably formulated and treated so as, once it contacts water at ambient temperature, said film dissolves after a predetermined period of time on the base of the characteristic average technical times of any building structure.
Said water-soluble plastic films are finally coupled, for protection purposes, to a mechanical reinforcement element which is respectively made of non-woven fabric on the dry side directed to the surface to be made impervious, and in biodegradable kraft paper or in thermoformed non-woven fabric on the side which directly contacts the external environment.
The layer which is placed on the dry side, and thus directed towards the surface to be made impervious, is advantageously made of thermoformed non-woven fabric based on low molecular weight polyester, and has a suitable open structure in order to allow the passage of the hydrated bentonite, i.e. the bentonite in its gel phase.
According to a further form of embodiment, said layer made of non-woven fabric can be replaced by a fabric layer having suitable weft, warping and weight.
Said gel, passing through said non-woven fabric and permanently burying the latter, realizes in this way the structure/leakproofing matrix cited above.
Moreover, said layer gives the underlying water-soluble film a mechanical protection, notably during the panel transport and/or assemblying operations.
According to the present invention the layers constituting the panel are advantageously joined together by using a water-soluble glue having physical-chemical characteristics which are equivalent to those of the water-soluble plastic film wrapping the honey-comb shaped inner layer.
Furthermore, it is possible to realize the coupling of the layers constituting the panel by using non water-soluble glues provided that they are not continuously and uniformly spread.
This means that the non water-soluble glue layer must be distributed in such a way as to leave some free areas on the surface interested to the glueing operation, said free areas allowing the passage of the water and of the bentonite as disclosed above.
When said layers are superimposed to each other according to the cited sequence, the panel is then completed by sealing the longitudinal and cross edges of the water-soluble plastic films by thermal welding and/or glueing by means of water-soluble and/or non water-soluble glues.
The panel-shaped form of embodiment according to the present invention is particularly used as leakproofing barrier in building of underground structures, tunnels and any other complex structures, such as submarine works.
Said panels can also have different shapes, they do not compulsory show a square cross-section, and they can also be very long (up to a hundred meters or more).
A further form of embodiment of the present invention provides for a article having a kerb or bead shape, which is particularly suitable for the impermeabilization of casting shut joints.
According to said form of embodiment, pure bentonite and/or bentonitic composition and/or any other leakproofing material in powder form and/or as a mixture, is filled inside of an envelope which advantageously has a cylindrical shape.
Said envelope is made of water-soluble plastic material which is leakproofing for a predetermined period of time as previously described with reference to the panel-shaped form of embodiment.
These envelopes can be made of different and specific dimensions according to the different building and/or application needs, and they are then produced in small dimensions (generally not longer than one meter), or wrapped in rolls up to some meters long.
Said kerbs are cheap and easy to be placed, e.g. by using fastening elements made of thermoformable plastic material or of electric welded metallic nets.